This invention relates to an ultrasonic scanner used in an ultrasonic diagnostic apparatus.
A tomogram of tissue of a living body can be obtained by irradiating an ultrasonic wave to the tissue. Namely, differences in structure between portions of the tissue lead to differing attenuation of the ultrasonic wave. Thus, the tomogram may be obtained by utilizing the echo of the irradiated ultrasonic wave. Ultrasonic diagnostic apparatuses based on this principle have been developed and applied to various medical fields.
Where an ultrasonic diagnostic apparatus is used for obtaining a tomogram of the heart, a proximity method is employed in general so as to prevent the influences of the ribs. The proximity method is a technique where an ultrasonic probe is settled as close as possible to the surface of the body under examination so as to enable the ultrasonic beam to be scanned through the space between two adjacent ribs.
The ultrasonic beam can be scanned in two ways; linear scan and sector scan. The sector scan is directed to the manner of scanning the ultrasonic beam by shaking the ultrasonic probe in a sector form. When it is intended to obtain a tomogram of the heart by the promixity method which necessitates scanning the beam through a very small space between two adjacent ribs, the sector scan is very effective.
Appended FIG. 1 shows a conventional ultrasonic high speed scanner performing sector scan, which is disclosed in the U.S. Pat. No. 3,927,661. As shown in the drawing, a pulley 2 is fixed to the shaft of a motor 1, said shaft being supported by a bearing 3. Further, an ultrasonic probe holder 6 and a pulley 7 are fixed to a transmission shaft 4 supported by bearings 5 and 5' and a transmission belt 8 is stretched between the pulleys 2 and 7. Still further, an ultrasonic probe 9 emitting and receiving an ultrasonic beam is mounted to the probe holder 6. The motor 1 is driven in clockwise and counterclockwise directions alternately and this particular rotation of the motor is transmitted to the transmission shaft 4 via the transmission belt 8 and the pulleys 2,7. Accordingly, the ultrasonic probe 9 fixed to the transmission shaft 4 is allowed to perform the sector scan.
The device of FIG. 1, however, is not satisfactory in that the ultrasonic probe fails to perform the sector scan at a high speed. In addition, the motor must provide a large torque, thereby rendering the entire device bulky. It should be noted in this connection that the ultrasonic scanner must be light and small because the scanner is hand held for operation particularly where the proximity method is applied for the diagnosis of the heart.
Also known is an ultrasonic scanner in which the rotation of the motor is converted to a rotatingly reciprocating motion, i.e., a head-shaking motion, of the ultrasonic probe by using a link mechanism. The scanner of this type, however, is defective in that the head-shaking motion lacks smoothness, rendering it difficult to enlarge the head-shaking angle of the probe, and that it is difficult to detect the scanning angle of the beam in spite of the fact that the angle detection is necessary for obtaining the image of the reflected beam.
As described previously, the ultrasonic diagnosis makes it necessary in general to settle the ultrasonic probe as close as possible to the surface of the body under examination. To achieve this, there is an effective technique referred to as the immersion method, namely, the ultrasonic probe is immersed in a transmission medium of the ultrasonic beam such as water, castor oil or liquid paraffin housed in a vessel. The vessel filled with the liquid mentioned is disposed in contact with the surface of the body under examination so as to enable the ultrasonic beam to be transmitted and received through the liquid-filled vessel. In this case, the vessel itself must be hand held in operating the ultrasonic scanner. Thus, it is customary in this immersion method to seal the vessel so as to prevent the liquid acting as the ultrasonic beam transmitting medium from spilling therefrom. Attention should be paid here to the aspect that the ultrasonic probe should perform the head-shaking motion within the vessel filled with the transmission medium of the ultrasonic beam. Naturally, it is necessary to reduce the power consumption of the apparatus in order to minimize the size of the apparatus. For example, the apparatus of FIG. 1 should be constructed such that the right hand portion divided by the dotted line a is disposed outside of the vessel. When it comes to the apparatus equipped with a link mechanism, it is necessary to dispose the link mechanism outside of the vessel. A major problem involved in these structures is that the rotatingly reciprocating motion generated outside of the vessel should be transmitted to the ultrasonic probe disposed within the vessel. Needless to say, it is quite difficult to seal the vessel in a manner to permit the transmission of the rotatingly reciprocating motion.